This application relates generally to gas turbine engines and, more particularly, to variable bypass valve systems used with gas turbine engines.
At least some known gas turbine engines include a fan upstream from a core engine that includes, in serial flow relationship, a low pressure compressor, or a booster, and a high pressure compressor. The low pressure compressor and the high pressure compressor compress airflow entering the combustor through the fan, with the airflow moving through an inlet section and a discharge section of the booster and then through an inlet section and a discharge section of the high pressure compressor. The booster is designed to facilitate providing optimal airflow to the high pressure compressor above a specific design throttle setting. At throttle settings off design, the booster may supply more air than the high pressure compressor can flow, which can lead to unsteady airflow in the engine.
To facilitate mitigating the effects of unsteady airflow, at least some known gas turbine engines include variable bleed valve (VBV) systems which rotate bypass doors open during unsteady airflow conditions to allow booster airflow to exit and bypass the high pressure compressor. The bleed doors and valves facilitate protecting the booster and high pressure compressor from eventual aerodynamic stall. At least some known VBV systems include a unison ring that is supported by dedicated ring supports extending from the booster frame structure. The structural supports facilitate preventing the unison ring from deforming excessively during operational loading. Excessive deformation of the unison ring may cause high stresses to be induced into the VBV system, which over time may lead to premature failure of the VBV system.
The unison ring is connected to two actuator bellcranks and ten door bellcranks. Rotation of the actuator bellcranks by action of a hydraulic actuator causes the ring to rotate, and thus subsequent rotation of the doors. The bellcranks are connected to the doors through clevis and spherical bearing attachments. In the ring to bellcrank connections, ring bushings extend between each bellcrank and the unison ring, and are positioned relative to the bellcranks such that a pre-determined gap is defined between each ring bushing and each bellcrank.
Assembling a known VBV system that includes dedicated ring supports may be a time consuming and tedious process, as the width of the gap between the ring ID and the dedicated supports is facilitated to be minimized. As the gap becomes smaller, assembly of the booster, including the dedicated supports, becomes more difficult as the supports must be inserted inside an inner diameter of the unison ring. However, if the gap is excessively large, the ring will not be adequately supported to minimize system stresses. Additionally in at least some known systems, the width of the bellcrank to bushing gap is predefined to be large enough to facilitate minimizing contact between the ring bushings and each bellcrank during operation. However, widening the gap increases an overall size of the VBV system which increases a cost and weight of the VBV system.
Assembling the VBV system may be time consuming and tedious process, as the width of the gap is optimized. Specifically, in at least some known systems, the width of the gap is predefined to be large enough to facilitate minimizing contact between the ring bushings and each bellcrank during operation. However, widening the gap increases an overall size of the VBV system which increases a cost and weight of the VBV system. On the other hand, although minimizing the width of the gap increases the effectiveness of the dedicated structural supports, the decreased width makes assembly of the VBV much more difficult, and also increases the chances for undesirable contact between the bellcrank and the ring bushings.
In one aspect, a method for assembling a gas turbine engine variable bypass valve system is provided. The method comprises positioning a unison ring circumferentially within the gas turbine engine such that the unison ring is radially outward from a structural frame, coupling at least one bellcrank to the unison ring, such that the unison ring is radially supported only by said at least one bellcrank, and coupling the at least one bellcrank to a bellcrank support that is coupled to the structural frame.
In another aspect of the invention, a variable bypass valve (VBV) system for a gas turbine engine is provided. The VBV system comprises a plurality of bellcranks spaced circumferentially within the gas turbine engine, and an annular unison ring coupled to the plurality of bellcranks for controlling the position of the plurality of bellcranks. The unison ring is radially supported only by the plurality of bellcranks.
In a further aspect, a gas turbine engine is provided. The gas turbine includes a structural frame and a variable bypass valve (VBV) system for selectively controlling air flowing through at least a portion of the engine. The structural frame extends circumferentially within the gas turbine engine. The variable bypass valve (VBV) system includes at least one bellcrank rotatably coupled to the structural frame, and an annular unison ring that is coupled to the bellcrank such that the unison ring is radially supported only by the bellcrank. The unison ring is for selectively controlling actuation of the bellcrank.